Ultra high frequency radio transmitter



Dec. 26, 1950 R. s. HOPE ULTRA HIGH FREQUENCY RADIO TRANSMITTER 2 Sheets-Sheet 1 Filed June 7, 1947 Dec. 26 1950 5, on; 2,535,067

ULTRA HIGH FREQUENCY RADIO TRANSMITTER Filed June 7, 1947 2 Sheets-Sheet 2 In enlur Altar/11:3."

Patented Dec. 26, 1950 ULTRA HIGH FREQUENCY RADIO TRANSMITTER Ronald Springford Hope, London, England, assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application June 7, 1947, Serial No. 753,305 In Great Britain March 15, 1946 Section 1, Public Law 690, August 8, 1946 Patent expires March 15, 1966 Claims.

This invention relates to radio transmission systems. More particularly, it relates to transmitting and radiating arrangements suitable for systems operating at very short wavelengths.

It is an object of the invention to provide a compact oscillation-generating and radiating unit employing a slot aerial.

It is a further object of the invention to provide a compact frequency modulated oscillationgenerator and radiator unit employing a slot aerial and specially suitable for use in a radio altimeter of the frequency sweep type.

According to the invention there is provided an ultra-high-fre uency radio transmitter unit comprising a resonating section of coaxial transmission line having a radiating slot aerial in the outer conductor, said resonating section being closed at each end by a screening header and being excited by a thermionic valve oscillator mounted within the transmission line and header assembly.

The invention further provides, for use in a radio altimeter system of the frequency sweep type, a transmitter unit according to the preceding paragraph in which one transmitted frequency by variation of the capacity between the header and the inner conductor of the said resonating section, the said capacity being formed between fixed condenser vanes on the said inner conductor and condenser vanes on the header rotated by an electric motor within the header.

Other objects and features of the invention will become apparentfrom the following detailed description of a preferred embodiment of the invention taken in conjunction with the accompanying drawings, in which- Fig. 1 is an exploded perspective view of an 18 cm. wavelength oscillation-generating and radiating unit in accordance with the invention, with certain parts cut away in order better to show the interior construction.

Fig. 2 is a perspective view of the assembled unit illustrated in Fig. 1.

In these drawings a given reference numeral refers to the same part in both figures.

Referring now to Fig. 1, the unit comprises a resonating section of coaxial" transmission line having an inner conductor I and an outer conductor or shell 2, the outer conductor being substantially one quarter wavelength in diameter and having located thereon a radiating slot aerial 3, only part of which is visible in the figure. This slot is arranged transversely i. e. in a plane perpendicular to the axis of the resonant coaxial line, opposite a voltage mode on the coaxial resonator, has a width of the order of one hundredth of a wavelength, and subtends an angle of substantially on the surface of shell 2, the length being thus rather less than one quarter of a wavelength at the operating frequency. The inner conductor I is supported within the outer conductor 2 by insulators 4 spaced round a circumference of the shell at intervals. One end of the coaxial line is closed by a metallic header 5 which is adjustably mounted on and galvanically connected to the shell 2 by screwthread means. Within the header 5 is mounted a small electric motor the shaft of which extends through the face 6 of the header and carries two butterfly condenser vanes 1. The header 5 is mounted within shell 2 at such a distance along the axis of the resonator that the capacity formed between the end of inner conductor 1, which carries two fixed butterfly condenser vanes 1 machined on its end surface, and the header-face 6 with condenser vanes l in the reference position, serves to tune the resonator to the reference frequency.

The resonating coaxial section is excited by a valve 9 which is mounted in the assembly with its longitudinal axis colinear with the axis of the resonating section. This valve, of a type already known in the art, is a triode with grid and anode connections brought out by disc seals to annular contacts encircling the glass envelope as shown at 10 and H, while the cathode heater connections are brought out as the inner and outer conductors I2 and I 3 of a coaxial line, the cathode itself being joined to the conductor 12 within the valve. Also within the valve are two small metal probes connected to the cathode and passing through the grid into the anodegrid space, providing feedback whereby sustained oscillations may be set up without any external feedback circuit.

The valve 9 is mounted in the transmitter unit by inserting the anode end of the valve envelope into the recess M in the inner conductor until the anode disc seal annulus H rests on the shoulder I5, against which it is then clamped by clamping ring I! which threadably-engages with the inner conductor. Thereafter the oathode header l6 pressed over the remainder of the valve to coinplete the grid, cathode, and header connections in the following manner.

The cathode header l7 comprises a metal washer 18, ring [9 of mica or other suitable insulating material, a metal spring washer 2 a metal back plate 2|, the cathode connector line assembly 22, and clamping ring 23;"references i8 ,5 apex of their V configuration, while the outer edges are bounded by the plates 34 and 35.

It will be understood however that even if the corner reflector composed of plates 3 and 35 is not fitted the corner reflector composed of plates 38 and All may still be fitted, in which case it could for example be secured to brackets radiating from shell 2 with an included angle of 90".

Still referring to Fig. 2, it will be observed that the ends of the slot are slightly enlarged and arcuate in shape, the radius of the are being about twice the width of the slot at its centre. This shaping of the ends, and the choice of the most suitable length and width, should be governed by the desirability of obtaining a good impedance match between the radiative load and the osci latory system comprising the valve and the coaxial resonator the efiective impedance of which, as viewed by the valve, is determined by the coupling of the radiation load via the slot aerial.

Since the assembly containing the valve is closed at the ends by the two headers it is advisable to make provision for dissipating the heat generated in the valve in the form of cathode heater power, anode losses, and the like. In the present embodiment of the invention this provision takes the form of an aperture in the cathode header through which cooling air may be forced under pressure over the grid and anode seals through a number of short slits in the clamping devices, the heated air being expelled through the slot aerial.

While the invention has been described with reference to an embodiment using a particular type of valve, it is to be understood that other types of valve suitable for the purpose may be emp oyed. For example, a valve may be used in which the feedback probes are connected to the anode instead of to the cathode, or in which no feedback probes are used at all, the feedback being obtained through the normal inter-electrode capacities.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:

1. An ultra high frequency radio transmitter unit comprising a resonant section of a coaxial transmission line, a screening header closing each end of said section, a thermionic valve having at least a cathode, an anode, and a control grid electrode energised from external sources, said anode and grid electrodes having disc seals coupled respectively to the inner and outer conductors of said resonating section at one end, and a transverse slot aerial in said outer conductor arranged parallel to and adjacent the connection between said grid disc seal and said outer conductor.

2. A radio transmitter unit according to claim 1 further comprising at least one probe electrode disposed part y within the cathode-grid space and partly within the grids anode space and connected to one of said valve electrodes other than the grid for feeding back energy in said valve to sustain oscil ations therein.

3. A radio transmitter unit according to claim 1, wherein the inner conductor of said resonating section is recessed to receive that part of the envelope of said thermionic valve extending from the anode seal away from the cathode end, and is galvanically coupled to said anode.

4. A radio transmitter unit according to claim 1 wherein the header at the excited end of said resonatng section is adapted to receive that part of the envelope of thermionic valve extending from the grid seal in the direction of the cathode, and is adapted to couple said grid to the outer conductor of said resonating section through capacity having negligible reactance at the operating wavelength.

5. A radio transmitter unit according to claim 1 wherein the header at the excited end of said resonating section comprises transmission line means for connecting the cathode heater system of sa d valve to energising terminals mounted on said header, said terminals having between them capacity of negligible reactance at the operating wavelength, the conductors between said terminals and said heater forming in conjunction with said terminal capacity a quarter wave transmission line filter.

6. A radio transmitter unit according to claim 1, furth r comprising a corner r flector system symmetrically positioned about the longitudinal axis of said slot aerial, said corner reflector system comprising two substantially flat metallic plates each radially mounted on said outer conductor and in galvanic contact therewith for substantially the whole length of one edge, the angle included by said plates being of the order of and the l n th of said contacting edge being substantially one half wavelength.

7. A radio transmitter according to claim 1, further comprising a corner reflector system symmet rically position d with respect to the ends of said slot aerial. said corner reflector system comprising two substantially flat metallic plates in planes forming a V configuration with apex line in the transverse plane containing said slot aerial, the angle included by said plates being of the order of 90, each plate having an edge contiguous to the surface of said outer conductor and being galvanically connected thereto in such manner as to short-circuit any parasitic slots of substan ial magnitude.

8. A radio transmitter unit accordin to claim 1 further comprising a first corner reflector system symmetrically positioned about the longitudinal axis of said slot aerial. said corner reflector system ComDliSlllg two substantially flat metallic plates each radially mounted on said outer conductor and in galvanic contact therewith for substantially the whole length of one edge. the angle included by said plates being of the order of 90; and the length of said contacting edge being substantially one half wavelength, and a second corner reflector system symmetrically positioned with respect to the ends of said slot aerial, said second corner refl ctor system comprising two substantially flat metallic plates in planes forming a V configuration wth apex line in the transverse plane containing said slot aerial. the an le included between said plates being substantially 90, each plate having an edge contiguous to the surface of said outer conductor and being galvanicallv connected thereto to shortcircuit any parasitic slots of substantial magnitude, the plates of both said corner reflector systems being galvanically connected together and extending outwardly substantially one half wavelength from the axis of said resonating section of coaxial transmission line.

9. An ultra high frequency radio transmitter unit comprising a resonant section of a coaxial transmission line, a screening header closing each end of said section, a thermionic valve having at least a cathode, an anode, and a control rams-mm igrid 'eleetjrode ,$fi$I{g'lSd from external :seurees, saidrz-ancde and grid eiectrodesa-havir gz disc seals woqpleidx-respectively=to the. inner and outer-econ- :ductors of said-resonating section 'at one end, eand a transversesslot :aerial insaid-uou-ter conductor: arranged parallel to and adiacent the connect-ion betweenesaid egridadisc sseai and .said

outer conductor and capacitive meansabetween uthe header:remote;-from-ithe excitedsend .of said eresonating section and the :innerconductor of meanscomprisesrotatablei-condenserwaneahav- .i-ng variables-capacity tofixed [condenser wanes non ssaid sinner conductor, wand which (said 7 header comprises-an electric motoriadapted to rotate said rotatable vanes and-,therebyvcyclically modulate the" frequency of the transmitter unit -throughthe required frequency sweep. RONALDSPRINGFORD .HOBE.

CES= CITED The. following .ref.erences...are .of recordrin the -.file .of this patent ITEDSSTAT-ES PATENTS Number Name Date 22219169 George, Oct. 21,1940 2412,4 16 DeWalt Dec. 10,1946 2,412,805 Ford .Dec. 17,.1946 "2314366 *Lin'denblad Jan. 14,1947 2,416,567 .McAr'thur .Feb. 25, 194'? 2,429,811 Guanere 'Oct. 28, 1947 2,436,398 "Morton Feb. '24, 194.8 2,436,930 Sharp'less 'Mar. 2,. 1948 "2,415,825 "Guarrera boat. '19, 1948 '2;4,58,6,50 Schreiner et a1. Jan. 11,1949 

